String cleaner, gimmick or not?

As the title already says, are products like GHS Fast Fret (mods, not sure if mentioning actual products is allowed? ) actually useful?
Do they improve the sound/playability of your instrument? Or even just lengthen the lifespan of strings? Or are they more a gimmick?

worth checking out this thread Fast Fret - any good?

Another recent thread: Coated Strings & String Conditioner

Yeah, stupid of me, when I pressed “post” I was thinking “probably should’ve done a proper search first”. :sweat:

I guess this thread can probably be closed.


Another one here.
Is this product good for keeping strings clean / lubed?